LAUSR

ABSTRACT The main purpose of this paper is to study osmotic dehydration of apple in water and sucrose solutions. The kinetics of water quantity and solid gain are described by two mathematical models using numerical solutions of the two-dimensional diffusion equation in Cartesian coordinates with boundary condition of third kind. For the first model, both the process parameters and the product dimensions have been considered constant. For the second model these quantities have been taken as variable. The numerical solutions have been obtained via the finite volume method with fully implicit formulation. Process parameter estimation, using experimental data, was obtained by an optimizer based on the inverse method. The third-kind boundary condition was shown to be appropriate in view of the fact that the resistances to mass flows on the product surface are not at all negligible. The temperature and concentration of the osmotic solution used in the experiments influenced significantly the kinetics of solid uptake and water quantity as well as the values of estimated parameters. Mathematical model which considers the variations in the process parameters and the product shrinkage presents good physical consistency and well describes the mass migrations.